Seeing at night has considerable evolutionary advantages both for predators and prey, and many mammals, including humans, have excellent night vision. Humans can perceive dim light flashes that produce single photon absorption in about 1 in 100 rods, which indicates that signals generated by single photons are reliably transmitted through the retina to the brain. We have a detailed understanding about how the rod photoreceptors encode single photons as electrical signals, but relatively little is known about how these tiny signals are transmitted through the retina. The general goal of this research is to gain a quantitative understanding of single photon synaptic transmission through the retina. We will use the mouse as a model system, because they have a well-developed night vision, and make an excellent model system for mammalian rod vision. Recordings of single photon signals will be made from each neuron in the chain of neurons connecting the rods to the ganglion cells. Voltage and current signals generated in response to dim light flashes will be analyzed. Specific aims include 1) determining the mechanisms of gain control at the rod synapse, 2) determining the nature of the non-linearity that controls convergent noise in the rod All amacrine cells, 3) resolving the single photon signal in ganglion cells. Advances in our understanding of normal retinal function will improve our understanding of the dysfunctions that result from retinal disease. Our resultswill have particular relevance to diseases that cause night blindness.